Security alarm systems are now widely used to protect domestic and business premises. One of the major problems with security alarm systems is the occurrence of false alarms which result not only in annoyance to neighbors but may endanger lives if remote notification, usually by means of a telephone dialler, to police, security organizations or an owner is effected. False alarms may be so persistent that the owner becomes afraid or embarrassed to use the system thereby completely negating the primary function of the system.
False alarms are usually quite random in nature and may be caused by taxi radio signals, CB radio signals, amateur radio signals and other occurrences. Prior art attempts to reduce false alarms included the use of pulse counting techniques which allowed the alarm to sound only after a number of pulses caused by an intrusion or the like during a given time. This technique may be applied either at the control unit or at the detector but leads to a reduction in the overall security offered by the system, particularly if the detector has a low range or limited view of the area, thus allowing an intruder to enter without the alarm sounding. Pulse counters may also hide the problem of a faulty detector even with control units which "memory latch" previous alarms.